Battery condition determination

ABSTRACT

An energy conversion arrangement configured to convert chemical energy into electrical energy. The energy conversion arrangement comprises plural cell groups 30, 32, 34, 36, each cell group being configured to convert chemical energy into electrical energy. The energy conversion arrangement also comprises at least one measurement arrangement 38, 40, 42, 44, 46 configured to make measurements at each of the plural cell groups 30, 32, 34, 36. Each energy conversion arrangement is configured to determine a condition of at least one of: each of the plural cell groups; and the energy conversion arrangement. The condition is determined in dependence on the measurements made at each cell group and a model of each cell group.

This application is a continuation of U.S. patent application Ser. No.15/308,092 filed on Oct. 31, 2016, which is a 371 of InternationalApplication No. PCT/GB2015/051308, filed on May 5, 2015, which claimsthe priority of Great Britain Application No. 1407805.9, filed on May 2,2014.

FIELD OF THE INVENTION

The present invention relates to an energy conversion arrangement, suchas an electric battery, which is configured to convert chemical energyinto electrical energy and to determine a condition of the energyconversion arrangement. The present invention also relates to a methodof determining a condition of an energy conversion arrangement which isconfigured to convert chemical energy into electrical energy. Thepresent invention further relates to a condition determining arrangementconfigured to determine a condition of an energy conversion arrangement.

BACKGROUND ART

Lithium-ion battery cells have seen widespread use in small consumerdevices such as laptop computers and mobile telephones. Lithium-ionbatteries have recently begun to supplant conventional batteries inapplications having greater electrical energy demands, such aselectrical vehicles and static electricity generation apparatus.Lithium-ion batteries are seeing increased use on account of theirnormally superior performance over conventional batteries, such aslead-acid and NiMH batteries, in particular in respect of energy storagedensity and power density. To meet electrical energy demand in suchlarger energy demand applications a battery is typically comprised ofplural lithium-ion battery cells which are arranged in at least one ofseries and parallel depending on current and voltage requirements.

Lithium-ion batteries can be dangerous under certain conditions onaccount of their containing a flammable electrolyte. Safe and effectiveuse of a lithium-ion battery normally requires operation of the batterywithin its Safe Operating Area (SOA). Considering operation within a SOAfurther, most lithium-ion cells are damaged if discharged below acertain voltage and their lifetime is reduced if discharged at too higha current or if charged too quickly. Furthermore lithium-ion cells maybe damaged if they are overcharged above a certain voltage or if theyexceed a certain temperature and may burst into flames if furtherovercharged. In addition there is often the lesser constraint of aNormal Operating Area (NOA). Breaching the NOA results in reduction incapacity or cell life over time. These challenges are compounded by themulti-cell configuration of the typical lithium-ion battery whereinunevenness of charge and discharge can arise between cells. Carefulmanagement by way of a battery management system (BMS) is thereforenormally required to provide for safe and effective operation.

Battery management systems for lithium-ion battery arrangements areknown. Such a battery management system typically makes measurements ofproperties, such as current, voltage and temperature, in a battery andmakes determinations concerning safe and effective operation based onthe measurements. The determinations are often made in dependence on ananalytical model of the battery.

The present inventors have become appreciative of shortcomings in knownapproaches to management of lithium-ion battery arrangements. Thepresent invention has been devised in the light of the inventors'appreciation of such shortcomings. It is therefore an object for thepresent invention to provide an improved energy conversion arrangementcomprising plural cells which are each configured to convert chemicalenergy into electrical energy, the energy conversion arrangement beingconfigured to determine a condition of the plural cells. It is a furtherobject for the present invention to provide an improved method ofdetermining a condition of an energy conversion arrangement comprisingplural cells. It is a yet further object for the present invention toprovide an improved condition determining arrangement configured todetermine a condition of an energy conversion arrangement comprisingplural cells.

STATEMENT OF INVENTION

According to a first aspect of the present invention there is providedan energy conversion arrangement, such as an electric battery,configured to convert chemical energy into electrical energy, the energyconversion arrangement comprising:

-   -   plural cell groups comprised in the energy conversion        arrangement, each cell group being configured to convert        chemical energy into electrical energy; and    -   at least one measurement arrangement configured to make        measurements at each of the plural cell groups,    -   the energy conversion arrangement being configured to determine        a condition of at least one of: each of the plural cell groups;        and the energy conversion arrangement, in dependence on the        measurements made at each cell group and a model of each cell        group.

An energy conversion arrangement according to the present invention,such as an electric battery, comprises plural cell groups which are eachconfigured to convert chemical energy into electrical energy whereby theenergy conversion arrangement may provide electrical energy from all ofthe plural cell groups. In the energy conversion arrangement at leastone measurement arrangement is configured to make measurements at eachof the plural cell groups. The measurements may, for example, comprisevoltage, current, temperature and pressure. Separate measurements aretherefore made for each of the plural cell groups. The energy conversionarrangement is configured to determine at least one condition, such asState of Charge (SOC), State of Health (SOH), Depth of Discharge (DOD),capacity, internal resistance and internal impedance, of each of theplural cell groups. The condition may thus comprise derived data, i.e.data derived from measurement of electrical and/or physical propertiesby the at least one measurement arrangement. Derived data may correspondto a property which is not susceptible to direct measurement. Thederived data may comprise at least one derived electrical property, suchas internal resistance or internal impedance. Alternatively or inaddition the derived data may comprise condition data representing anoperational condition of at least one of a cell group and the energyconversion arrangement, such as SOC, SOH or DOD. The condition of atleast one of: each of the plural cell groups; and the energy conversionarrangement is determined in dependence on the measurements made at eachcell group and a model of each cell group. In a distributed arrangement,as described further below, the condition of each cell group may bedetermined in dependence on the measurements made at the cell group anda model of the cell group. The energy conversion arrangement maytherefore be operative to determine a separate condition for each cellgroup.

A cell group model may be determined in dependence on measurements madeon a cell group, such as during initial tests. The cell group model maytherefore be a numerical model in contrast with known analytical modelsalbeit battery level models. Where the energy conversion arrangementcomprises an electric battery, the cell group model may be based onmeasurements sufficient to characterise a SOC versus Open CircuitVoltage (OCV) curve for the electric battery. Each cell group model maybe stored at the cell group. Typically and as described further belowmeasurement apparatus and analogue-to-digital conversion apparatus alsomay be located at the cell group in view of the convenience of using adigital cell group model as opposed to an analogue cell group model.According to one approach, the same cell group model may be used foreach cell group. According to another approach, a different cell groupmodel may be used for each cell group. More specifically each cell groupmodel may be configured for the cell group with which it operates, suchas in dependence on measurements made at the cell group during initialtesting/calibration. Nevertheless the cell group model may be of a samestructure.

The energy conversion arrangement may be further configured to determinea condition of the energy conversion arrangement per se in dependence onthe plural cell group conditions. The overall condition may thereforedepend on the determined condition of all the separately determined cellgroup conditions. For example and where the energy conversionarrangement comprises an electric battery an overall SOC and an overalldepth of discharge for the battery may be determined. Furthermore abetter informed decision may be made in respect of an operation on theenergy conversion arrangement, such as when to perform charge balancing.The energy conversion arrangement may comprise an energy conversionarrangement model which, in use, receives the plural cell groupconditions and provides energy conversion arrangement data in dependencethereon. The condition of the energy conversion arrangement per se maybe determined in dependence on the energy conversion arrangement data.According to one approach, the energy conversion arrangement model maybe stored at one location, such as at one of the cell groups. Accordingto another approach, there may be at least one copy of the energyconversion arrangement model which is stored at a different locationsuch as at another one of the cell groups. For example there may be asmany copies of the energy conversion arrangement model as there are cellgroups with a copy being stored at each of the cell groups. Having atleast one copy of the energy conversion arrangement model stored asdescribed above may reduce the amount of data that is required to becommunicated within the energy conversion arrangement.

As mentioned above, charge balancing may be an important function for anenergy conversion arrangement, such as an electric battery. Knownapproaches to charge balancing are described in Battery ManagementSystems for Large Lithium-Ion Battery Packs, Davide Andrea, 2010,published by Artech House, Norwood Mass. 02062, USA. As describedelsewhere herein the energy conversion arrangement according to thepresent invention may be configured such that each cell group determinesits own SOC. Furthermore each cell group receives, amongst other things,SOC data for other cell groups comprised in the energy conversionarrangement whereby an SOC for the energy conversion arrangement may bedetermined. The energy conversion arrangement may be configured suchthat each cell group is operative to determine whether or not the cellgroup should perform passive charge balancing in dependence on the cellgroup's own SOC and the SOC for the energy conversion arrangement. Thuseach cell group in the energy conversion arrangement makes adetermination in respect of charge balancing either independently of theother cell groups or in cooperation with the other cell groups.Nevertheless the energy conversion arrangement may be configured suchthat determinations in respect charge balancing are made on adistributed basis and without dependence on a central controller. Indeedand as described elsewhere herein the energy conversion arrangement maylack any central controller. A central controller is characteristic ofknown centrally controlled energy conversion arrangements which contrastwith the distributed approach of the present invention. The energyconversion arrangement of the present invention may be configured toperform charge balancing in dependence on a determination made by a cellgroup. The energy conversion arrangement may therefore comprise chargebalancing apparatus. The form and function of appropriate chargebalancing apparatus is described in Battery Management Systems for LargeLithium-Ion Battery Packs.

Alternatively or in addition the energy conversion arrangement may beconfigured for active charge balancing.

Known battery management systems rely on a battery model whereas thepresent invention relies on a cell group model. Management according tothe present invention can therefore take the characteristics ofindividual cell groups into consideration, for example, to monitorindividual cell groups over time. Monitoring individual cell groups overtime enables determination of the like of a rate of reduction of stateof health of a particular cell group that is greater than a rate ofreduction of state of health of another cell group. A weak or exhaustedcell group may therefore be identified with greater ease prior to itsreplacement in preference to more involved investigation to determinethe weak or exhausted cell group or replacement of all the cells groupswhere only one cell group might need replacing. Furthermore monitoringindividual cell groups over time may upon analysis yield information ofassistance in addressing a warranty issue or detecting performance thatis progressing towards a potentially dangerous condition such as athermal event, for example, a fire. In addition monitoring individualcell groups may provide for the generation of alarm data when adetermined condition passes a threshold, such as when a SOC drops belowa predetermined value. The energy conversion arrangement may thereforebe operative to store, for example in non-volatile memory, a pluralityof conditions determined at spaced apart times. Condition data stored atone time may comprise at least one of: number of completecharge/discharge cycles; total coulomb transfer; temperature, such asmaximum and minimum temperature; SOC; SOH; DOD; and capacity. Morefundamental condition data may also be stored such as at least one ofvoltage, current, resistance and impedance. Condition data stored at anyone time may comprise a time stamp. Where determination and storage ofcell group condition is at each cell group, as described further below,monitoring over time may provide for storage of condition data even ifthe energy conversion arrangement is incompletely assembled or if anenergy conversion arrangement management system, such as a BMS, ispowered down.

The energy conversion arrangement may be further operative to analysethe stored plurality of conditions, for example, to determine the likeof a trend. Alternatively or in addition, analysis may be performedother than in the energy conversion arrangement. The energy conversionarrangement may therefore be configured, such as by way of acommunications port, to provide for the stored plurality of conditionsto be conveyed away from the energy conversion arrangement to furtherapparatus, such as computing apparatus comprised in the like of abattery charging station or in a remote server, for analysis in andreporting by the further apparatus.

Storage of a plurality of conditions determined at spaced apart timesmay provide for ease of use of the energy conversion arrangement in asecond application after its initial application. For example, initialuse in BEVs may require operation of an electric battery at over 80% oforiginal capacity whereas operation of the battery at over 50% oforiginal capacity may be sufficient for a second use such as in off-gridstorage subject to the service history as reflected by the storedconditions being at least satisfactory. The energy conversionarrangement may therefore be operative to determine electrical energydelivery capacity, such as storage capacity when the energy conversionarrangement is a battery. The energy conversion arrangement may befurther operative to compare the electrical energy delivery capacitywith a predetermined value and perhaps also to determine if the energyconversion arrangement should be subject to second use. Alternatively orin addition the energy conversion arrangement may be operative todetermine whether or not a service history is at least satisfactory independence on the stored plurality of conditions and perhaps also todetermine if the energy conversion arrangement should be subject tosecond use. Re-use of energy conversion arrangements as local storage inoff-grid applications may be beneficial in smoothing variation in demandand supply and improving upon efficiency and in particular where thereare plural energy sources which provide for fluctuation in supply, suchas local wind, solar and CHP generation plant.

As mentioned above, lithium-ion battery cells can be dangerous undercertain conditions on account of their containing a flammableelectrolyte. Appropriate design is therefore required of lithium-ionbattery cells to provide for their safe use. It is not unknown for animproperly designed or manufactured lithium-ion battery cell to beunwittingly brought into use with the nature of the improper design notbeing evident from ordinary inspection of the battery cell. Verificationof properly designed lithium-ion battery cells may therefore beadvantageous to mitigate risk, support product warranties and present abarrier to the introduction of counterfeit batteries. The model of eachcell group may therefore further comprise an identification code whichis unique to each cell group. Each cell group may thus be identifiableand susceptible to verification. Furthermore and where each cell groupmodel comprises an identification code, each cell group may be readilyidentified and distinguished from the other cell groups within theenergy conversion arrangement to thereby provide for ease of removal ofa cell group from the energy conversion arrangement during a replacementprocedure. The cell group model may further comprise a cryptographicsigning component to thereby provide for cell group authentication and,where there is storage of a plurality of conditions determined at spacedapart times, for verification of stored condition data.

The value of lithium-ion battery cells is relatively high. Battery theftis therefore a risk. As mentioned above, the energy conversionarrangement may be configured, such as by way of a communications port,to provide for conveyance of data away from the energy conversionarrangement to the like of a battery charging station. Suchcommunication may provide for tracing of a stolen battery by way of itsunique identification code. The identification code may comprise aunique address. The identification code may be in a standard electroniccommunications format and perhaps an Internet protocol such as TCPprotocol over IPv6. Use of a standard electronic communications formatmay provide for ease of communication of data between the energyconversion arrangement and the like of an Internet based database. Suchan Internet based database may be operative to store data from aplurality of energy conversion arrangements over time with such storeddata being of value to the like of cell and energy conversionarrangement manufacturers. A unique address may provide for addressingof individual cell groups within the energy conversion arrangement whenthe cell groups are comprised within a wider communications network suchas may be provided when the energy conversion arrangement is incommunication with the like of a battery charging station.

Management according to the present invention can take thecharacteristics of individual cell groups into consideration to providefor improved determination of state of charge (SOC). Improveddetermination of SOC may provide an improvement in operation vis-à-visan SOA. Advantages include improved battery use, such as increasedoperating range before re-charge when the energy conversion arrangementis comprised in a battery electric vehicle or more reliable end of lifedetermination.

The energy conversion arrangement may comprise a network and may beconfigured such that each of the plural cell groups is connected to thenetwork. Communication over the network may be by way of an Internetprotocol, such as TCP/IP. The network may comprise an isolated busarrangement whereby the plural cell groups are of equal priority. Asmentioned above, each cell group model may comprise an address whereby acell group can be identified by way of its address instead of by itsphysical location. During assembly, cell groups of an energy conversionarrangement may therefore be installed in any order. Furthermore a cellgroup may be replaced without the need to reassign its location in thenetwork. An isolated bus approach provides, in contrast with isolatednode communications, for substantially constant communication latencybetween any two cell groups.

The energy conversion arrangement may comprise plural measurementarrangements with each measurement arrangement being configured to makemeasurements at a respective one of the plural cell groups. Each of theplural measurement arrangements may be located at a respective one ofthe plural cell groups. There may therefore be less communication withinthe energy conversion arrangement with attendant benefits such asreduction in susceptibility to interference where communication is byelectrical wires. The energy conversion arrangement may further compriseanalogue-to-digital conversion apparatus which is operative to receiveanalogue signals from the at least one measurement arrangement andprovide corresponding digital signals. Where the energy conversionarrangement comprises plural measurement arrangements, there may beplural analogue-to-digital conversion apparatus with eachanalogue-to-digital conversion apparatus being operative to receiveanalogue signals from a respective measurement arrangement. Eachanalogue-to-digital conversion apparatus may be located with ameasurement arrangement at a different cell group. Conversion to digitalsignals may therefore take place at the cell group. Having such adistributed architecture may reduce calibration and test overheads. Forexample BMS calibration and test may be performed at least in part atthe same time as group cell test.

Each cell group may comprise plural cells, such as two or four electricbattery cells. The energy conversion arrangement may typically compriseplural cells which may be arranged in parallel to form a block whichprovides increased current with plural cells or blocks being arranged inseries to increase the voltage. A cell group may therefore be a block. Acell may be considered as the most basic element in the energyconversion arrangement that is capable of producing electrical energy independence on chemical energy. The plural cells in a cell group maytherefore be treated as an entity with regard to measurement and a cellgroup model. Alternatively at least one cell group may comprise solelyone cell. Measurements may therefore be made in respect of only one celland the cell group model may be for one cell only.

The plural cell groups are comprised in an energy conversion arrangementwhich is configured to convert chemical energy into electrical energy.The energy conversion arrangement may comprise energy storage apparatus.The energy storage apparatus may comprise an electric battery and maythus be operative in dependence on stored chemical energy. The energyconversion arrangement may be operable to convert electrical energy intostored chemical energy. The electric battery may therefore be asecondary electric battery, i.e. a rechargeable electric battery. Atleast one cell may be an electrochemical cell which is operative toconvert stored chemical energy into electrical energy and vice-versa.More specifically the at least one cell may be a lithium-ion (Li-ion)cell. Alternatively the energy conversion arrangement may be operativeon chemical energy from received rather than stored matter. The energyconversion arrangement may therefore comprise a fuel cell arrangement.The fuel cell arrangement may be operative to convert received fuel,such as hydrogen, into electrical energy. At least one cell may be afuel cell.

Measurements may comprise measurements of at least one of an electricalproperty and a physical property. Measurements may comprise: voltage;current; temperature; and pressure. The at least one measurementarrangement may be appropriately configured to measure the at least oneelectrical property and physical property.

Where the energy conversion arrangement comprises an electric battery,the energy conversion arrangement may be configured to determine how theelectric battery is to be charged in dependence on at least onedetermined condition. More specifically the energy conversionarrangement may be configured to determine how the electric battery isto be charged having regards to SOA requirements to provide, forexample, fast charging but without compromising the integrity or safetyof the electric battery. The energy conversion arrangement may thereforecomprise parameters relating to SOA requirements. A determination as tohow the electric battery is charged may be in dependence on servicehistory as reflected by a stored plurality of conditions, as describeelsewhere herein. An intended use of the energy conversion arrangementafter charging may have a bearing on how the electric battery ischarged. The energy conversion arrangement may therefore comprise anoperator input which is user operable to input data relating to intendeduse and data storage and which is operative to store data input by theuser. Where the energy conversion arrangement is to be used in a BEV,the user may, for example, input data relating to an intended distanceto be travelled by the BEV. The energy conversion arrangement may beoperative to determine how the electric battery is charged in dependenceon the data input by the user. Different energy tariffs may apply atdifferent times of the day. It may therefore be advantageous to controlwhen the electric battery is charged. Control over when the electricbattery is charged may be by way of the operator input described above.The energy conversion arrangement may further comprise chargingapparatus which is configured to charge an electric battery comprised inthe energy conversion arrangement. The charging apparatus may becontrolled in dependence on operation of the energy conversionarrangement as described elsewhere herein.

As described elsewhere herein, each cell group may be operative per sein respect of management functions such as: measurement of the like ofvoltage, current and temperature; determination of various parameterssuch as SOC, DOD, SOH and internal resistance; and the recordal ofevents such as charge/discharge cycles, NOA and SOA excursions. Eachcell group may be so operative irrespective of whether the energyconversion arrangement has yet to be assembled from the cell group andother cell groups, the energy conversion arrangement has been assembledor the energy conversion arrangement has been disassembled. Each cellgroup may therefore be configured to perform at least one managementfunction. Alternatively or in addition, each cell group may beconfigured to perform at least one management function in cooperationwith at least one other cell group.

According to a second aspect of the present invention there is providedan electric vehicle (EV) comprising an energy conversion arrangementaccording to the first aspect of the present invention. An electricvehicle (EV) may comprise an electric propulsion arrangement. The EV mayeither comprise an electric battery or lack an electric battery. Morespecifically the electric vehicle may be one of a fuel cell electricvehicle (FCEV), a Battery Electric Vehicle (BEV), a Hybrid ElectricVehicle (HEV) and a Plug-in Hybrid Electric Vehicles (PHEV). Where theelectric vehicle comprises an electric battery, the electric vehicle mayfurther comprise charging apparatus which is configured to charge theelectric battery.

It is known for an electric vehicle to comprise a data recorder which isoperative to record data relating to use of the electric vehicle. Oftenonly relatively recent data is stored in the data recorder such as datarelating to the most recent five seconds of use of the electric vehiclebefore an impact. The energy conversion arrangement may be configuredeither alone or in combination with the data recorder to provide forenhanced data recording. More specifically the energy conversionarrangement may be configured to record, in addition to cell groupcondition, measurements from at least one in-vehicle sensor, such asmeasurements relating to GPS location, speed and acceleration.

The energy conversion arrangement may be configured to analyse recordeddata and to compare an outcome of the analysis with reference data. Thereference data may, for example, be based on data recorded during atleast one previous journey and the analysis may comprise comparingefficiency of energy use between a presently completed journey and thereference data. By way of further example, the reference data may bebased on data collected from plural energy conversion arrangements whichis received from a server operative to receive and store data recordedby plural energy conversion arrangements. A user of the energyconversion arrangement may thus be able to compare driving efficiencywith the like of a mean standard established by a large number of othervehicles for a similar journey.

According to a third aspect of the present invention there is providedenergy conversion arrangement management apparatus comprising pluralenergy conversion arrangements each according to the first aspect of thepresent invention and a server, each energy conversion arrangement andthe server being configured to be in data communication with each other.More specifically the server may be configured to store energyconversion arrangement management data. The energy conversionarrangement management data may comprise data received from each of theplural energy conversion arrangements. The energy conversion arrangementmanagement data may be of value to manufacturers and suppliers for thelike of: dealing with warranty issues; authentication of cell groups;and evaluating product performance. Alternatively or in addition, anenergy conversion arrangement may receive and be operative in dependenceon energy conversion arrangement management data received from theserver. For example, a user of the energy conversion arrangement may beadvised of a need for servicing of the energy conversion arrangement orof appropriate journey planning in dependence on energy conversionarrangement management data received from the server.

According to a fourth aspect of the present invention there is provideda method of determining a condition of an energy conversion arrangement,such as an electric battery, configured to convert chemical energy intoelectrical energy and comprising plural cells which are each configuredto convert chemical energy into electrical energy, the methodcomprising:

-   -   making measurements at each of the plural cells; and    -   determining a condition of at least one of: each of the plural        cell groups; and        the energy conversion arrangement, in dependence on measurements        made at each cell and a model of each cell.

Embodiments of the fourth aspect of the present invention may compriseone or more features of any previous aspect of the present invention.

According to a fifth aspect of the present invention there is provided acondition determining arrangement comprising:

-   -   at least one measurement arrangement configured to make        measurements at each of plural cell groups comprised in an        energy conversion arrangement, each of the plural cell groups        being configured to convert chemical energy into electrical        energy; and    -   a computer program comprising program instructions for causing a        computer, such as a microcontroller, to determine a condition of        at least one of: each of the plural cell groups; and the energy        conversion arrangement, in dependence on the measurements made        at each cell group and a model of each cell group.

More specifically the computer program may be one of: embodied on arecord medium; embodied in a read only memory; stored in a computermemory; and carried on an electrical carried signal. Further embodimentsof the fifth aspect of the present invention may comprise one or morefeatures of the first aspect of the present invention.

According to a further aspect of the present invention there is providedan energy conversion arrangement comprising: plural cell groups, eachcell group being configured to convert chemical energy into electricalenergy; and at least one measurement arrangement configured to makemeasurements at each of the plural cell groups, the energy conversionarrangement being configured to determine a condition of the energyconversion arrangement in dependence on the measurements made at eachcell group. The energy conversion arrangement may be configured todetermine a condition of at least one cell group in dependence on themeasurements made at each cell group. Further embodiments of the furtheraspect of the present invention may comprise one or more features of anyprevious aspect of the present invention.

BRIEF DESCRIPTION OF DRAWINGS

Further features and advantages of the present invention will becomeapparent from the following specific description, which is given by wayof example only and with reference to the accompanying drawings, inwhich:

FIG. 1 shows an Electric Vehicle comprising an energy conversionarrangement according to the present invention during charging;

FIG. 2 is a block diagram representation of an energy conversionarrangement according to the present invention;

FIG. 3 is a block diagram representation of circuitry of the energyconversion arrangement which is located at a cell block;

FIG. 4 is a block diagram representation showing cell group models and abattery model; and

FIG. 5 illustrates a cycle of use of a battery cell.

DESCRIPTION OF EMBODIMENTS

A Battery Electric Vehicle (BEV) 10 comprising an energy conversionarrangement 12 in the form of an electric battery according to thepresent invention is shown in FIG. 1 while the electric battery is beingcharged. As can be seen from FIG. 1, the BEV 10 further comprisescharging apparatus 14 which is electrically coupled to the electricbattery 12 and which is operative to control the charging of theelectric battery. In accordance with known practice the chargingapparatus 14 is electrically connected to a vehicle charging point 16.The vehicle charging point 16 is in communication with a remote server18. Data is communicated between the vehicle charging point 16 and theserver 18 as is described further below. Plural further vehicle chargingpoints 20 are provided at respective different locations with eachfurther vehicle charging point 20 also being in communication with theserver 18 whereby data from each of the vehicle charging points 16, 20is conveyed to, stored in and operated upon by the server 18. FIG. 1shows an arrangement involving charging by way of a wired couplingbetween the charging point 16 and the energy conversion arrangement 12.According to an alternative approach charging is wireless by way of aninductive coupling between the charging point 16 and the energyconversion arrangement 12. The design of an inductively coupled wirelesscharging arrangement will be within the ordinary design capabilities ofthe person of ordinary skill in the art. As can be seen from FIG. 1, theelectric battery 12 comprises sixteen blocks 22 of lithium-ion batterycells (which each constitute a cell group) which are connected inseries. Each block 22 comprises plural lithium-ion battery cells whichare connected in parallel. In an alternative form each block comprisessolely one battery cell it being noted that the present invention isequally applicable when solely one battery cell is used instead ofplural battery cells. The electric battery 12 further comprises abattery management arrangement 24 which is described further below withreference to FIGS. 2 to 4.

A block diagram representation of four series connected blocks oflithium-ion battery cells and associated circuitry (which togetherconstitute an energy conversion arrangement) is shown in FIG. 2. Thearrangement of FIG. 2 comprises first, second, third and fourth blocksof cells 30, 32, 34, 36. The arrangement of FIG. 2 further comprisesfirst, second, third and fourth measurement and processing circuitry 31,33, 35, 37 which are each at a respective one of the first, second,third and fourth blocks of cells 30, 32, 34, 36. The first, second,third and fourth measurement and processing circuitry 31, 33, 35, 37 aresubstantially the same as one another. One of the first, second, thirdand fourth measurement and processing circuitry 31, 33, 35, 37 is shownin more detail in FIG. 3. The measurement and processing circuitry ofFIG. 3 comprises a low value resistor 38 in series with each block whichis operative to sense the current drawn from the block and which formspart of a voltage divider arrangement (not shown) which is operative toconvert the drawn current to a measurable voltage. Measurement is to 12or 14 bit accuracy with the actual accuracy to which the current isdetermined being less than afforded by 12 or 14 bit measurement onaccount of the effect of self heating. A first analogue-to-digitalconverter 40 is operative to convert the voltage from the voltagedivider arrangement to corresponding digital data. The measurement andprocessing circuitry of FIG. 3 also comprises a secondanalogue-to-digital converter 42 which is operative to convert thevoltage across the block to corresponding digital data. The voltageacross the block is measured to within 1 mV. The measurement andprocessing circuitry of FIG. 3 also comprises a temperature sensor 44such as a silicon bandgap temperature sensor (or Proportional ToAbsolute Temperature [PTAT] sensor) comprised in an integrated circuitor a discrete thermistor, which is disposed on or near the block andthus is operative to sense the temperature of the block. A thirdanalogue-to-digital converter 46 is operative to convert the analoguesignal from the temperature sensor 44 to corresponding digital data.Temperature is measured to 0.5 degrees Centigrade.

The measurement and processing circuitry of FIG. 3 yet further comprisesa microcontroller 48, non-volatile RAM 50, a Real Time Clock (RTC) 52and transceiver circuitry 54. Components of the measurement andprocessing circuitry of FIG. 3 other than the microcontroller 48 areconstituted as a custom integrated circuit with the measurement andprocessing circuitry being contained within or mounted on the block. Themicrocontroller 48 receives digital data from the first to thirdanalogue-to-digital converters 40, 42, 46 corresponding to current,voltage and temperature and is operative to process the received dataand to determine block conditions and electrical parameters as describedbelow. As will become apparent from the following description conditiondetermination involves comparison with threshold values. The measurementand processing circuitry of FIG. 3 therefore comprises a stable voltagereference, such as a band-gap reference, which is calibrated against aknown voltage. The determined conditions and derived electricalparameters are stored in the non-volatile RAM 50 along with a time stampfrom the RTC 52 whereby data is stored for the lifetime of the block.The measurement and processing circuitry of FIG. 3 is operative tomeasure the voltage, current and temperature at a rate between 0.01 Hz(i.e. less than once per minute) and 1 kHz depending on system activity.When there is no charging or discharging, measurement is at a very slowrate to minimise power consumption. On the other hand, measurement is ata higher rate when there is activity such as charging or discharging.The microcontroller 48 is operative to prioritise stored data andperiodically deletes old data or data of less significance to therebymake efficient use of the non-volatile RAM 50. The RTC 52 is autonomousand is driven by either a quartz crystal oscillator or a timing signalfrom the microcontroller 48. Whatever long term drift may be present isaddressed by periodically synchronising the RTC 52 to an external clocksuch as an Internet based clock service accessed by way of the vehiclecharging point 16. The measurement and processing circuitry of FIG. 3 isoperative to detect when no current is drawn by a block whereupon themeasurement and processing circuitry enters a sleep state from which itawakes periodically to resume measurement.

Onward communication of data from the measurement and processingcircuitry of FIG. 3 is by way of the transceiver circuitry 54 to a bus56. The transceiver circuitry 54 is configured to provide galvanicisolation from the bus 56. Galvanic isolation is employed to address thecumulative voltage shift as the bus 56 traverses all the blocks in thebattery. In a first form, the transceiver circuitry 54 is configured tocommunicate by way of the IEEE 802.15 Personal Area Network standardwith data being conveyed by way of twisted-pair cable connected by atransformer (not shown) to each transceiver circuitry 54. In a secondform, data is conveyed by way of the main electrical battery bus. Themain electrical battery bus is normally noisy and therefore a robustprotocol of a kind used in Power Line Communications (PLC) is employedin the second form instead of the IEEE 802.15 Personal Area Networkstandard.

Returning now to FIG. 2, a supervisory microcontroller 58 is connectedto the bus 56. The supervisory microcontroller 58 is configured toperform supervisory operations in relation to the measurement andprocessing circuitry of FIG. 3 at its respective block of cells 30, 32,34, 36. The supervisory microcontroller 58 is either one of themicrocontrollers at a block of cells or a separate microcontroller. Thesupervisory microcontroller 58 is configured to provide forcommunication with an external network which is accessed when theElectric Vehicle 10 of FIG. 1 is connected to the vehicle charging point16. Communication of data with the external network is by way of a wiredchannel or a wireless channel depending on whether charging is achievedby way of a wired approach or a wireless approach. As mentioned abovewith reference to FIG. 1 there is data communication between the vehiclecharging point 16 and the server 18. The supervisory microcontroller 58is configured to provide for communication with the external network inaccordance with an Internet protocol such as TCP protocol over IPv6. Useof an Internet protocol provides for ease of communication of databetween the supervisory microcontroller 58 and the server 18. The server18 of FIG. 1 is operative to store data from a large number of BEVs overtime with such stored data being of value to the like of cell and energyconversion arrangement manufacturers. The supervisory microcontroller 58is further configured to cooperate with other on-board measurement anddata recording apparatus whereby data from in-vehicle sensors and thelike is received by the supervisory microcontroller 58 for onwardcommunication to the server to provide for enhanced data recording. Thesupervisory microcontroller 58 is further configured to analyse recordeddata and to compare an outcome of the analysis with reference data. Thereference data is, for example, based on data recorded during at leastone previous journey and the analysis comprises comparing efficiency ofenergy use between a presently completed journey and the reference data.By way of further example, the reference data may be based on datacollected from several BEVs which is stored in the server 18 andsubsequently communicated to the BEV which is making use of a facilityto compare driving efficiency with the like of a mean standardestablished for a similar journey by a large number of other vehicles.

A unique address is stored in memory local to each microcontrollerwhereby each block can be uniquely identified. The unique address has aformat in accordance with an Internet protocol such as TCP protocol overIPv6 to thereby provide for ease of communication of data by way of thebus 56 between each block and an Internet connected server 18.

The processing of measurements within the first to fourth measurementand processing circuitry 31, 33, 35, 37 will now be considered in moredetail with reference to FIG. 4. FIG. 4 is a block diagramrepresentation of cell group models and a battery model. FIG. 4 showsthe first and second measurement and processing circuitry 31, 33 fortheir respective blocks. Components in common with FIGS. 2 and 3 areindicated by like reference numerals. Also shown in FIG. 4 is a firstcell group model 60, a second cell group model 62, a first battery model64 and a second battery model 66. The first cell group model 60 isstored in memory local to a first microcontroller of the firstmeasurement and processing circuitry 31 for one block and the secondcell group model 62 is stored in memory local to a secondmicrocontroller of the second measurement and processing circuitry 33for the other block. The first battery model 64 is stored in memorylocal to the first microcontroller and the second battery model 66 isstored in memory local to the second microcontroller. There is thereforea cell group model and a battery model at each block of battery cells.The same battery model is present at each block of battery cells suchthat in the present example the second battery model 66 is a copy of thefirst battery model 64. As will become apparent from the followingdescription, each battery model 64, 66 makes use of data produced byboth of the cell group models 60, 62. Data from each cell group model60, 62 is therefore conveyed by way of the bus 56 to both battery models64, 66.

Operation of a cell group model will now be described. As describedabove voltage, current and temperature data is received by themicrocontroller. The microcontroller is then operative to determineblock conditions and derived electrical parameters in dependence on themeasured voltage, current and temperature data with reference to a cellgroup model. More specifically block conditions and derived electricalparameters include the like of State of Charge (SOC), State of Health(SOH), Depth of Discharge (DOD), capacity, internal resistance andinternal impedance. Block conditions further include events such as SOAand NOA infringements and charge/discharge cycles. An example of a modelfor a cell group or an individual battery cell which is employed incondition determination is provided below. Outputs from the cell groupmodel are then conveyed to the battery model which is operative todetermine the like of overall SOC, overall SOH, overall DOD, overallcapacity, overall internal resistance and overall temperature for thebattery in dependence on the outputs received from cell group models 60,62. A microcontroller at a block is then further operative to act independence on the battery level determinations. As a consequence of thepresence of a battery model in each of the first to fourth measurementand processing circuitry 31, 33, 35, 37, each block is capable ofindependent operation in respect of the battery as a whole. For exampleeach microcontroller is operative to determine the requirement for andthen to initiate and control a charge balancing operation.

Charge balancing is often an important function for an electric battery.As described above each cell group determines its own SOC and receives,amongst other things, SOC data for other cell groups comprised in theelectric battery whereby an SOC for the battery as a whole isdetermined. The battery is configured such that each cell group isoperative to determine whether or not the cell group should performpassive charge balancing in dependence on the cell group's own SOC andthe SOC for the battery. Thus each cell group in the battery makes adetermination in respect of charge balancing either independently of theother cell groups or in cooperation with the other cell groups. Thebattery further comprises charge balancing apparatus which is operativein dependence on a determination being made in respect of chargebalancing. The form and function of appropriate charge balancingapparatus for use herein is described in Battery Management Systems forLarge Lithium-Ion Battery Packs, Davide Andrea, 2010, published byArtech House, Norwood Mass. 02062, USA.

A cell group or an individual battery cell is modelled by way of thefollowing algorithm. The inputs to the algorithm are:

-   1. The nominal full cell capacity, CapCell.-   2. The present cell Depth of Discharge (DOD) in Ah. If the cell is    full then DOD=0. If the cell is empty then DOD=CapCell.-   3. The nominal cell resistance, Rcell_nom.-   4. The cell open circuit voltage (OCV) at four appropriate points in    the State of Charge (SOC) versus OCV curve for the cell. For    example, the four appropriate points are: the voltage at SOCempty    0%=Vempty; the voltage at SOCbottom 15%=Vbottom, the voltage at    SOCtop 95%=Vtop; and the voltage at SOCfull 100%=Vfull. The OCV is    the cell terminal voltage when no current is drawn and when the cell    has had time to relax.

The algorithm has two independent loops, Loop 1 and Loop 2.

Loop 1:

-   -   When the drawn current changes, calculate the cell resistance,        Rcell, on the basis of Rcell=(V1−V2)/(I2−I1), where V1 and I1        are the voltage and current measured before the current change        and V2 and I2 are the voltage and current measured after the        current change.    -   The instantaneous OCV is determined by OCV=Vterm+Icell*Rcell,        where Vterm is the measured instantaneous terminal voltage and        Icell is the measured instantaneous current.

Loop 2:

● IF charging (i.e. current, I < 0) THEN ● Calculate OCV = Vterm +Icell * Rcell ● IF OCV < Vtop THEN ● Integrate cell current, Icell, intothe DOD ● Convert DOD to SOC by way of SOC = 100% − 100 * DOD /  CapCell● IF SOC > SOCtop THEN ● Set SOC = SOCtop ● Convert SOC to DOD by way ofDOD = Capcell * (100% −  SOC) ● ELSE ● Convert OCV to SOC using astraight line interpolation between  SOCtop and SOCfull and between Vtopand Vfull ● Convert SOC to DOD ● IF discharging (current, I, > 0) THEN ●IF OCV > Vbottom THEN ● Integrate cell current into DOD ● Convert DOD toSOC ● IF SOC < SOCbottom THEN ● Set SOC = SOCbottom ● Convert SOC to DOD● ELSE ● Convert OCV to SOC using a straight line interpolation between SOCbottom and SOCempty and between Vbottom and Vempty ● Convert SOC toDOD

The above algorithm is given by way of example only. During use of thealgorithm there is an accumulation of errors on account of integrationof measured current to determine the DOD whereby the DOD measurementuncertainty normally increases over time. The algorithm thereforeinvolves a reset of the DOD when the SOC goes through either SOCtop orSOCbottom which can result in a significant jump in the measured SOC andDOD.

A battery is modelled by way of algorithms that provide for the like ofthe summing of individual cell block conditions, derived electricalparameters and measurements and the determination of derived quantitiessuch a mean or average based on summed quantities.

The cell group model described above is based on the State of Charge(SOC) versus open circuit voltage (OCV) curve for the cell block. Thecell group model for each cell block is configured and calibrated bytaking the cell block through at least one complete charge and dischargecycle. During the at least one complete cycle voltage, current,temperature and time are measured to high accuracy and the measuredvalues are used to configure and calibrate the cell group model. Eachcell group model is therefore configured specifically for a particularcell block. Normally the cell group model calibration is performed atthe same time as calibration of the rest of the battery managementsystem to thereby provide a simpler calibration procedure and otherwiseavoid duplication of cell group model calibration operations and batterymanagement system calibration operations.

A cycle of use of a battery cell is shown in FIG. 5. Upon manufacturethe cell 80 has an SOH of 100% and is installed in an electric batteryof a BEV 82. After a period of use in the BEV 82, the SOH of the cell asdetermined by the present invention drops to 80% which is a criticalthreshold for continued use in the BEV 82. Following identification ofcell weakness by the present invention, the cell is removed from the BEVand installed in local electric battery storage 86 in an off-gridenvironment. The local electric battery storage 86 is configured inaccordance with the present invention whereby monitoring of the cell iscontinued. When the SOH of the cell 88 as determined by the presentinvention drops to 50% which is a critical threshold for continued usein the local electric battery storage 86, the cell is removed from thelocal electric battery storage 86 and decommissioned 90.

It is to be noted that each cell group is operative of itself in respectof management functions such as: measurement of the like of voltage,current and temperature; determination of various parameters such asSOC, DOD, SOH and internal resistance; and the recordal of events suchas charge/discharge cycles, NOA and SOA excursions. Each cell group isso operative irrespective of whether the battery has yet to be assembledfrom the cell group and other cell groups, the battery has beenassembled or the battery has been disassembled such the cell group nolonger forms part of the battery. Each cell group is thereforeconfigured to perform the above described management functions.Furthermore each cell group is configured to perform the above describedmanagement functions in cooperation with at least one other cell group.

The present invention is also of application in Hybrid Electric Vehicles(HEVs), Plug-in Hybrid Electric Vehicles (PHEVs) and fuel cell electricvehicles (FCEVs). Where the present invention is applied to an FCEV,modifications are made to the cell/cell group model to take account ofthe different characteristics of fuel cells. Nevertheless models of thefuel cells comprised in the FCEV are determined in the same fashion asdescribed above with reference to battery cells by way of measurementsat each fuel cell during an initial calibration procedure. Furthermorethe nature of the condition data determined for the fuel cells isselected to cater for the different characteristics of fuel cells.Otherwise the invention is of a form and function as described abovewith reference to BEVs.

1. An energy conversion arrangement configured to convert chemical energy into electrical energy, the energy conversion arrangement comprising: plural cell groups, each cell group being configured to convert chemical energy into electrical energy; and at least one measurement arrangement configured to make measurements at each of the plural cell groups, the energy conversion arrangement being configured to determine a condition of at least one of: each of the plural cell groups; and the energy conversion arrangement, characterised in that the condition is determined in dependence on the measurements made at each cell group and a model of each cell group. 